In an electric power tool of the type including a speed reduction mechanism, use is made of a structure for changing the reduction ratio of the speed reduction mechanism. In this structure, a changeover member such as a ring gear included in a planetary gear mechanism is axially slid to change the engagement state of the planetary gear mechanism.
For example, Japanese Patent Application Publication Nos. 2009-56590 and 2009-78349 disclose electric power tools in which the slide movement of a changeover member including a ring gear is automatically carried out by a solenoid.
In the electric power tool capable of automatically changing the reduction ratio as mentioned above, however, it is sometimes the case that the changeover member fails to smoothly engage with a counterpart gear member when one attempts to bring the changeover member into sliding engagement with the counterpart gear member. In this case, the reduction ratio is not successfully changed, thereby hindering the works. Moreover, heavy load is applied to an actuator such as a solenoid for causing the slide movement of the changeover member. This may be a cause of trouble.